Aug 21 (Reuters) - Wall Street was set to open lower on Friday, with the S&P 500 mini futures falling to their weakest level since early February, as more alarming data from China spooked investors already worried about global growth.

The data from China showed its giant manufacturing sector slowing at the fastest pace since the depths of the financial crisis in 2009, confirming the worries about its health that have preying on economist's minds for months.

That decline comes on the heels of weaker-than-expected data in July, plus this month's turbulent changes in the yuan and a brutal stock market plunge. Shanghai stocks dropped another 4 percent on Friday.

World stock markets tumbled towards their worst week of the year on Friday and commodities had another bruising day.

"There are many, and legitimate, contributing factors to the global economic slowdown narrative. These include China-related issues, such as the recent devaluation of its currency, the stock market's boom and bust in recent months, and slower GDP growth," Nigel Green, CEO of deVere Group, said.

"I believe that this volatility is likely to remain with us, at least until the end of the year ... But for most long term investors, fears of a near-term financial apocalypse are overdone."

Dow e-minis were down 99 points, or 0.59 percent, with 59,555 contracts changing hands. Every one of the 30 Dow components were in the red in premarket trading.